Repository hosted by TU Delft Library

Home · Contact · About · Disclaimer ·
 

Observations of sand waves, megaripples, and hummocks in the Dutch coastal area and their relation to currents and combined flow conditions

Author: Passchier, S. · Kleinhans, M.G.
Type:article
Date:2005
Institution: TNO Bouw en Ondergrond
Source:Journal of Geophysical Research F: Earth Surface, 4, 110
Identifier: 238865
doi: doi:10.1029/2004JF000215
Article number: No.: F04S15
Keywords: bedform · climate conditions · coastal zone · current velocity · flow velocity · grain size · hummocky cross-stratification · marine environment · monitoring · ripple · sand wave · shallow water · spatial distribution · wind wave · Benelux · Eurasia · Europe · Netherlands · Western Europe · Lanice conchilega

Abstract

[1] This paper aims to investigate the distribution and stability of large-scale bed forms in response to storm and fair-weather conditions in a shallow marine environment. Multibeam and side-scan sonar data off the Dutch coast (median grain size 0.25-0.35 mm) were collected to monitor sand waves (λ = 100-800 m) and superimposed megaripples (λ = 1-40 m) through multiple storm and fair-weather events. Box cores were used to observe the vertical bed structure and grain size. In the Dutch coastal area, two-dimensional (2-D) megaripples (X = 1-15 m) are the dominant bed forms in current-dominated (>0.4 m/s) tidal flow regimes with oscillatory flows <0.15 m/s. Effects of trapping of fine material under these conditions by tube building Lanice conchilega colonies on bed form development are suspected but need further study. At slightly higher energy conditions, 3-D megaripples (λ = 5-15 m) begin to form on the shoreface. After seasonal storms, at oscillatory flows >0.4 m/s, undulating bed topography of mound-like 3-D bed forms (λ = 20-40 m) is observed. Immediately after storms, these bed forms are covered by smaller 3-D megaripples, which are related to sets of low-angle converging laminae in box cores, interpreted as hummocky cross stratification (HCS). The sand waves form compound bed forms of sets of 2-D and 3-D megaripples. The morphology of the sand waves is a function of the general wind-wave climate of the marine environmental setting, with flat-topped 3-D sand waves occurring in shallow wave-dominated settings and 2-D sand waves occurring in the tide-dominated environment farther offshore. Copyright 2005 by the American Geophysical Union.